This application claims the benefit of German Application DE P 10020664.6 filed Apr. 27, 2000, herein incorporated by reference.
When winding cheeses, a distinction is basically made between two types of windings: a. precision winding, and b. random winding. With precision winding, there is a constant relationship between the number of bobbin revolutions and the speed of the yarn cross winding during the entire bobbin travel, so that the winding ratio remains the same during the entire winding process. The yarn crossing angle decreases with increasing bobbin diameter. With random winding, there is a fixed relationship between the velocity of the peripheral or circumferential surface of the bobbin and the speed of yarn cross winding. The yarn crossing angle is kept constant by this relationship, while the winding ratio, i.e. the number of bobbin turns per double lift, becomes smaller with increasing diameter.
The present invention relates to a method for producing cheeses of a random winding type, particularly in a winding machine having a yarn guide drum and a creel that are mounted to be axially shiftable relative to each other and a ribbon disturbance device such that the relative movement between the yarn guide drum and the creel when the cheese enters a ribbon winding zone counteracts a stroke change caused by the ribbon disturbance device.
Automatic cheese winders having winding heads with yarn guide drums mounted in an axially shiftable manner are known, e.g., in German Patent Publication DE 43 36 312 A1. The yarn guide drum is connected to a drive shaft that also comprises the rotor of the bobbin drive device. Moreover, this known winding device comprises an edge displacement mechanism with which the yarn guide drum can be axially moved back and forth in a reciprocating, traversing manner as required with a constant stroke length.
German Patent Publication DE 198 29 597 A1 describes a method of producing cross-wound cheeses in a xe2x80x9crandomxe2x80x9d type of winding process. In order to avoid ribbon-like pattern windings the bearing pressure of the cheese on the yarn guide drum can be reduced and the cheese loaded at the same time with a braking moment. Thus, the angular velocity of the cheese is constantly detected and processed in a control device in such a manner that at or shortly before a ribbon winding zone is reached, the angular velocity of the cheese is lowered to a non-critical angular velocity by a defined adjusting of the bearing pressure with which the cheese rests on the yarn guide drum. A device for performing this method is disclosed in German Patent Publication DE 198 29 597 A1.
Cheeses produced in accordance with the previously described method are characterized by a clearly improved ribbon resolution as well as by a very good flow behavior even at high unwinding speeds in subsequent production processes.
However, the reduction of the bearing load of the cheese on the yarn guide drum in the ribbon winding zones results in a slight impairment of the visual appearance of such cheeses. In particular, as a result of the reduction of the bearing load in the ribbon winding zones, a slight reduction of the displacement width of the yarn traversed by the yarn guide drum (i.e., the stroke) can occur in these areas. Such a change in stroke becomes visible as rings on the ends of the bobbins of the cheeses.
It is accordingly an object of the present invention to improve the known devices for random winding in order to overcome the disadvantages discussed above and manufacture cheeses in which the external appearance corresponds to their high manufacturing quality.
The objective is achieved by the present invention which produces a cheese with the desired visual appearance by using a winding station having a yarn guide drum and a creel mounted in an axially shiftable manner relative to each other and a ribbon disturbance device such that when a cheese enters a ribbon winding zone, relative movements between the yarn guide drum and the creel counteracts a stroke change caused by the ribbon disturbance device.
The method of the present invention has the particular advantage that the stroke change occurring in the ribbon winding zones by a ribbon disturbance device during the placement of yarn windings is immediately compensated by the simultaneous introduction of a relative movement between the yarn guide drum and the creel.
A preferred embodiment of the present invention provides that the stroke losses occurring on account of the ribbon disturbance process during the placement of yarn windings are compensated in a simple manner by an axial oscillation of the yarn guide drum with an adjustable amplitude. This assures that the cheeses produced have neither rings nor other optical impairments on their bobbin flanks.
Preferably, the oscillation of the yarn guide drum takes place simultaneously with the slippage regulation causing the ribbon disturbance. Thus, as soon as the drive device for the creel lift-off device is activated by the winding-head computer to reduce the bearing pressure between the cheese and the yarn guide drum, the drive for axial displacement, or oscillation, of the yarn guide drum, is automatically activated.
In addition to the frequency of the oscillation, the amplitude of the oscillation of the yarn guide drum is very important for an unobjectionable bobbin flank of the cheese. Since both the frequency and the optimum amplitude of the oscillation are a function of different bobbin parameters, e.g., the yarn material, the bobbin hardness, etc., it is preferable if both the frequency and also the amplitude of the oscillation can be adjusted in a defined manner.
The frequency of the oscillation is relatively low, e.g., between about 0.1 and about 3 hertz with about 0.5 hertz being especially advantageous.
Since the magnitude of the amplitude of the oscillation is very significant for the later appearance of the bobbin flank of the cheese, the amplitude is preferably selected to reliably assure that the stroke loss resulting from the ribbon disturbance is regained during the later traversing of the yarn.
The yarn guide drum oscillation in accordance with the present invention occurs independently of the operation of a standard edge displacement device of the winding head.
In a preferred embodiment in which the standard edge displacement device is already in operation at the winding head, a superimposing of the standard edge displacement motion and the yarn-guide-drum oscillation occurs in accordance with the present invention. Hence, the amplitude of the standard edge displacement motion is increased by the amplitude of the yarn guide drum oscillation.
In the preferred embodiment, a stepping motor which drives the edge displacement device is programmed so that it can operate continuously in one direction or in a reversing manner during which the angle of rotation of the stepping motor can be adjusted in a defined manner. Thus, the present invention provides a simple way to adjust the frequency as well as the magnitude of the amplitude of the oscillation of the yarn guide drum in a defined manner without having to expand the hardware of the winding head, which is associated as a rule with not-insignificant expense.
Further details, features and advantages of the present invention will be understood from the following disclosure of exemplary embodiments with reference to the accompanying drawings.